Intracellular potentials of microperfused human sweat duct cells

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Abstract
Intracellular potentials of cells from isolated segments of microperfused human sweat ducts were measured in order to determine the electrical profiles of these cells under resting, transporting, and inhibited conditions. Even though the cells are relatively small (ca. 6–8 μm), continuous recordings of intracellular potentials from the same impalement were stable for up to 2 h. In the resting condition in normal Ringer's solution when the lumen of the duct was collapsed and not perfused, the intracellular potential measured across the basal membrane was 34.6±1.5 mV (n=31; mean±SE). In the same bathing medium, when the duct lumen was also perfused with normal Ringer's solution, the basolateral membrane potential (V b), the apical membrane potential (V a) and transepithelial potential (V t) was −33.8±0.47 mV, −23.7±0.48 mV and −9.6±0.9 mV (n=73), respectively. The average input impedence (R i) of these cells was 19.6±0.4 MΩ (n=36). The frequency distribution ofV b was unimodal suggesting that only one functional cell type exists in this tissue. Amiloride (0.1 mM) in the lumen hyperpolarized bothV a andV b by −40.5±3.6 mV and −33.2±3.7 mV (n=15), respectively, with a slight but significant increase inR i (15%), while abolishingV t. Removing luminal Cl− depolarizedV a by +37.0±4.2 mV and hyperpolarizedV b by −19.0±4.2 mV (n=11). Removing Cl− from the bath hyperpolarizedV a by −3.3±2.3 mV and depolarizedV b by +24.3±2.7 mV (n=15). Ouabain caused an initial fast depolarization (+8 mV) followed by a prolonged slow depolarization ofV b, and an increase inR i of about 84%. These results not only provide the first electrical profile of the human sweat duct tissue, but they also show that its cell membrane potentials are unusually low. This unusual property of this epithelium appears to be due to the combination of a significant Na+ conductance at the apical membrane and a remarkably high tissue Cl− conductance.